1. Field of the Invention
The present invention concerns a hearing device and a method for reduction of feedback therein between a speaker and a number of microphones.
2. Description of the Prior Art
In principle it is desirable to achieve together the following properties of a part of a hearing device located in the ear:                open feed        utilization of the natural directional effect of the pinna (auricle), i.e. microphone position in the auditory canal        freedom from feedback, or at least a low feedback tendency in the system.        
The desired properties or requirements cited above are conventionally achieved (each separately) according to the following:                The open feed is achieved with an open ear fitting piece given a behind the ear hearing device (BtE).        The natural directional effect of the pinna can be achieved by a complete CIC device located in the auditory canal, but a ventilation of the auditory canal can be achieved only with difficulty due to feedback problems.        The freedom from feedback can be attained by use of a circuit known as a feedback compensator that operates on the principle of counter-phase cancellation of the feedback signal. Due to the relatively high variability and complexity of the feedback path, the effect is conventionally limited to approximately 10 dB to a maximum of 15 dB amplifier gain. In order to achieve this, however, sealing of the auditory canal is generally necessary.        
Active noise suppression for a hearing aid device wearable in the ear is known from DE 103 32 119 B3. The device described therein has an additional earpiece that is arranged in a ventilation channel. This additional earpiece is located approximately in the middle of the ventilation channel, and two microphones are located symmetrically to this additional earpiece in the ventilation channel. One of the two microphones and the earpiece serve to prevent direct noise in the auditory canal and the additional microphone, together with the earpiece, serves to prevent feedback.
Furthermore, a noise suppression arrangement with focused adaptive filtering for hearing prostheses is known from DE 693 27 992 T2. The feedback suppression arrangement described therein has two microphones as well as a speaker.